"Cannot read property 'pop' of undefined" with a common cache group

[OscarBarrett]

I ran into this after upgrading to 0.4.2.

ERROR in chunk common [initial]
common.css
Cannot read property 'pop' of undefined
TypeError: Cannot read property 'pop' of undefined
    at MiniCssExtractPlugin.renderContentAsset (.../node_modules/mini-css-extract-plugin/dist/index.js:343:44)
    at Object.render (.../node_modules/mini-css-extract-plugin/dist/index.js:175:32)
    at Compilation.createChunkAssets (.../node_modules/webpack/lib/Compilation.js:2358:29)
    at hooks.optimizeTree.callAsync.err (.../node_modules/webpack/lib/Compilation.js:1268:10)
    at AsyncSeriesHook.eval [as callAsync] (eval at create (.../node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:6:1)
    at AsyncSeriesHook.lazyCompileHook [as _callAsync] (.../node_modules/tapable/lib/Hook.js:35:21)
    at Compilation.seal (.../node_modules/webpack/lib/Compilation.js:1213:27)
    at hooks.make.callAsync.err (.../node_modules/webpack/lib/Compiler.js:547:17)
    at _done (eval at create (.../node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:9:1)
    at _err16 (eval at create (.../node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:218:22)
    at _addModuleChain (.../node_modules/webpack/lib/Compilation.js:1064:12)
    at processModuleDependencies.err (.../node_modules/webpack/lib/Compilation.js:980:9)
    at _combinedTickCallback (internal/process/next_tick.js:131:7)
    at process._tickCallback (internal/process/next_tick.js:180:9)

common.css is set up like so:

optimization: {
  splitChunks: {
    cacheGroups: {
      common: {
        name: 'common',
        chunks: 'initial',
        minChunks: 3,
        priority: 10,
        reuseExistingChunk: true
      }
    }
  }
},

And has an explicit entry with the following:

common: [
  path.resolve(srcPath, 'vendor.scss'),
  path.resolve(srcPath, 'main.scss')
]

[alexander-akait]

@OscarBarrett Looks like a bug

[alx-web]

Same problem appeared after update to Babel 7 i don't know if there is a link

[raphaelbeckmann]

Same problem here even without a cache group.

Build fails with:

Cannot read property 'pop' of undefined
TypeError: Cannot read property 'pop' of undefined
at MiniCssExtractPlugin.renderContentAsset (node_modules/mini-css-extract-plugin/dist/index.js:343:44)

[alexander-akait]

Please create minimum reproducible test repo

[OscarBarrett]

https://github.com/OscarBarrett/mini-css-issue-257

yarn
yarn build

Note that the build succeeds if the common entry is commented out.

[ndisidore]

Ran into this today too.

webpack: 4.17.2
mini-css-extract-plugin: 0.4.2

Little more insight into what may be happening:

bestMatch never gets a value because sortedModules is empty (note that in my case, the function input param modules in renderContentAsset has 3 items in it).
This is because getModuleIndex2 returns undefined for every module that gets passed in (I verified this manually by running all the modules through it).

I was able to fix this by locally editing index.js and changing this if statement to always return false

mini-css-extract-plugin/src/index.js

Line 397 in dd141f2

if (typeof chunkGroup.getModuleIndex2 === 'function') {

So it looks like the fallback logic

mini-css-extract-plugin/src/index.js

Lines 480 to 485 in dd141f2

	// fallback for older webpack versions
	// (to avoid a breaking change)
	// TODO remove this in next mayor version
	// and increase minimum webpack version to 4.12.0
	modules.sort((a, b) => a.index2 - b.index2);
	usedModules = modules;

still works.

[alexander-akait]

@ndisidore feel free to send a PR 👍

[ndisidore]

I can totally help with a PR. May need a little direction on the correct way to do it vs the quick fix.

It looks like getModuleIndex2 is just a .get on the map of the chunkGroup. So essentially what we're trying to do is see if the current module is in the given chunk group. Under what circumstances would this never be the case and are those expected?

Some more context around those specifics.

[aganglada]

When will this get resolved? I'm running into the same issue here.

[alexander-akait]

@aganglada When somebody send a PR